1. Field of the Invention
An oil pan is typically provided with a baffle plate, which is used to eliminate entrapment of air in an oil strainer, such as a filtration oil filter, through oil inlets, as well as to prevent oil from sloshing around. Conventionally, the baffle plate is welded to the oil pan, or otherwise secured, together with the oil pan, to an engine block.
2. Description of Related Art
As is known from, for instance, U.S. Pat. No. 4,793,299, entitled "Engine Cylinder Block Reinforcing Structure," issued on Dec. 27, 1988, a reinforcing mechanism may be used to increase the strength of and reinforce skirts which project downward from the cylinder block to which the oil pan is attached. The reinforcing mechanism includes a plate-shaped reinforcing member, spanning and interconnecting portions ranging between a deep portion and a shallow portion of the oil pan, and a plate-shaped stiffening member for providing portions o flanges, integrally formed on lower ends of the skirts, corresponding to the shallow section of the oil pan, with a rigidity higher than that of portions of the flanges corresponding to the deep portion of the oil pan. The reinforcing mechanism is designed to have a weight of approximately 1% to 6% of the weight of cylinder block, and is connected, together with the oil pan, to the engine block. The reinforcing mechanism reinforces the cylinder block without substantially increasing the weight of the engine, and decreases engine vibrations and noises.
The known baffle plate fitting structure, however, if it is welded to the oil pan, tends to undesirably allow air to be admitted into the oil strainer through the oil inlets and be trapped. This is because the baffle plate, welded to the oil pan, must be placed so as not to conceal the oil strainer. Otherwise, if the baffle plate is fit between the oil pan and the cylinder block, the engine will possibly encounter oil leaks.
Known cylinder blocks may be divided into two block portions: an upper block portion, and a lower block portion, integrally formed with skirts and bearing caps, which is bolted to the upper block portion. Such a structure is known from, for instance, Japanese utility model application No. 60-153055, entitled "Engine Body Structure," filed on Oct. 4, 1985, and published as Japanese Unexamined Utility Model Publication No. 62-61960.
Generally, in a cylinder block having a lower cylinder block portion fitted to an upper cylinder block portion, the block portions are connected together by cylinder block portion fastening bolts. A change in an axial fitting or fastening force may be caused between the upper and lower cylinder blocks, due to a change in friction produced between the structural element and bolt heads of the cylinder block portion fastening bolts.
Further, in assembling known cylinder blocks, bearing bores for main bearing journals of a crankshaft are drilled only after the upper and lower cylinder block portions are rigidly fastened to each other by bearing cap fastening bolts and cylinder block fastening bolts. The upper and lower cylinder block portions are then disassembled for crankshaft installation. Thereafter, the upper and lower cylinder blocks, with the crankshaft installed therein, are fastened again by the fastening bolts. If the baffle plate, together with bearing caps of the lower cylinder block, are fastened to the upper cylinder blocks by the bearing cap fastening bolts, the bearing cap fastening bolts apply to the bearing caps a force which is different from the force applied when the bearing bores are drilled. This causes the bearing bore to be misshapen, or out-of-round, and, therefore, produces an insufficient clearance between the bearing bore and the main bearing journal of the crankshaft, which leads to seizing in the bearing.